1. Field of the Invention
This invention concerns peptides of short chain length (10, 11, 12 or 13 amino acids) which increase the immunological competence of mammals, especially human beings.
2. Prior Art
A number of substances are known which, when administered to mammals, enhance the ability of the organism's immune system to combat disease. Among these substances are crude extracts of mycobacteria, glycopeptides and modifications of glycopeptides which are derived therefrom, and "thymosins" a family of hormones secreted by the thymus gland. Recently, it has been shown that a fraction of blood, specifically, human serum prealbumin, also possesses such activity (U.S. Pat. No. 4,046,877).
The structure of human serum prealbumin is now clearly established. It is a tetramer of subunits, each of which contains 127 amino acids in the same known sequence (Kauda, Y., et al, J. Biol Chem., 249: 6796 (1974)); and even the three-dimensional configuration has been determined (Blake, C. L. F., et al, J. Mol. Biol., 121(3): 339 (1978). The sequence most relevant to the present invention is that of the N-terminal end, which has been shown to be: ##STR2## A nonapeptide fragment corresponding to the sequence starting at the N-terminal end of each subunit was reported in 1971 as part of earlier efforts to determine the prealbumin structure. (Gonzalez, G. et al, Biochem. J., 125: 309 (1971).
It has now been found, surprisingly, that the deca-, undeca-, dodeca- and tridecapeptides which represent the N-terminal sequence in human serum prealbumin subunits are extremely potent in increasing immunologic competence in mammals. Further, modification of the amino acid sequence of these peptides, at one or more positions by substituting another amino-acyl residue for that normally present, results in a set of peptides with similar or enhanced activity.